Common mode choke

ABSTRACT

A cable distribution plant is protected from noise where a modem housing includes a switching power supply and modem digital electronics, the switching power supply for receiving AC mains power from an AC supply via an EMI filter and the modem digital electronics for receiving a switching power supply output from the switching power supply via an LC filter for filtering noise at a switching power supply frequency wherein multiple switching noise filters communicate with respective modems at subscriber sites protect a head end from switching power supply harmonic noise otherwise aggregated by distribute nodes and passed to the head end.

PRIORITY

This application is a continuation in part of U.S. patent applicationSer. No. 16/171,803 filed Oct. 26, 2018 entitled Common Mode Choke. Thisapplication claims the benefit of U.S. Prov. Pat. App. No. 62/735,557filed Sep. 24, 2018 entitled Common Mode Choke.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an article of manufacture forattenuating electrical signals. In particular, a device preventsunwanted and/or spurious signals from propagating upstream in a cabledistribution system serving subscribers via coaxial cable.

Discussion of the Related Art

Filters are well-known devices for eliminating noise in electricalcircuits. In the cable television industry, these well-known filters aretypically placed inside electrical enclosures such as modem boxes. Thesefilter(s) assure that noise leaving the box is within acceptable limitsconsidering operation of subscriber equipment and considering operationof the cable distribution plant. Distribution of modem box filters toinclude filters inside the box and outside the box are not well-known.

SUMMARY OF THE INVENTION

The present invention provides a noise protection for a cabledistribution plant.

In an embodiment a cable distribution system includes devices forattenuating noise propagating upstream from multiple subscriber sitestoward a head end, the noise attenuating devices including a distributedcable modem filter and comprising: plural subscriber sites served by acable distribution system node and plural nodes served by a cabledistribution system head end; each subscriber site including an AC mainspowered modem interconnected with the node via a coaxial cable and eachnode interconnected with the head end via an optical fiber; a modemtransceiver receiving a broadcast signal originating from the cabledistribution system and transmitting a signal to one of a televisionfront end and a computer; within a modem housing a switching powersupply receiving AC mains power via an EMI filter and digitalelectronics receiving a switching power supply output via an LC filterfor filtering noise at a switching power supply frequency; and, externalto the modem housing and integrated with the coaxial cable, a discretecomponent filter for filtering noise at harmonics of the switching powersupply frequency, the noise carried by one or both of the coaxial shieldand the coaxial center conductor; wherein the discrete component filtersused with respective modems at subscriber sites protect the head endfrom switching power supply harmonic noise otherwise aggregated by thenodes and passed to the head end.

In some embodiments the system further comprises within the discretecomponent filter, a micro coaxial cable coiled around a ferrite in theform of a toroid; and a metal sleeve around the cable and ferrite, themetal sleeve contacting a coaxial connector at one end of the filter butdisconnected from a coaxial connector at the other end of the filter.

In some embodiments the system micro-coaxial cable has a braid shieldand a foil shield. And, in some embodiments the system is influenced bycapacitive effects owing to use of 1.5 mm diameter micro-coaxial cablecoiled about a ferrite contribute to filter response that is about flatbetween 15 and 35 MHz.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described with reference to the accompanyingfigures. These figures, incorporated herein and forming part of thespecification, illustrate embodiments of the invention and, togetherwith the description, further serve to explain its principles enabling aperson skilled in the relevant art to make and use the invention.

FIG. 1A shows a cable distribution plant.

FIG. 1B shows another view of a cable distribution plant.

FIG. 2A shows yet another view of a cable distribution plant.

FIG. 2B shows a cable modem block diagram.

FIG. 2C shows a power rail interconnection with a coaxial cable.

FIG. 3 shows a cable distribution plant with noise protection.

FIG. 4A shows an auxiliary filtering device for filtering coaxial shieldnoise for use in the cable distribution plant of FIG. 3.

FIG. 4B a cross-sectional view of an embodiment of the filter of FIG.4A.

FIG. 4C shows response of an embodiment of the filter of FIG. 4B.

FIG. 5A shows another auxiliary filtering device for filtering coaxialshield noise for use in the cable distribution plant of FIG. 3.

FIG. 5B shows yet another auxiliary filtering device for filteringcoaxial shield noise for use in the cable distribution plant of FIG. 3.

FIG. 6A shows an auxiliary filtering device for filtering coaxial shieldnoise and coaxial center conductor noise for use in the cabledistribution plant of FIG. 3.

FIG. 6B shows another auxiliary filtering device for filtering coaxialshield noise and coaxial center conductor noise for use in the cabledistribution plant of FIG. 3.

FIG. 7 shows a ferrite for surrounding a modem power cable and a modemcoaxial cable for filtering noise on a coaxial shield for use in thecable distribution plant of FIG. 3 in lieu of the inline filteringdevice shown.

FIG. 8A-B show an isolating filter and its printed circuit boards usedas an auxiliary filtering device for filtering noise on a coaxial shieldfor use in the cable distribution plant of FIG. 3.

FIG. 8C shows a response curve for a selected filter.

FIGS. 9A-E show a first case design for the filter.

FIGS. 10A-E show a second case design for the filter.

FIGS. 11A-D show a third case design for the filter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The disclosure provided herein describes examples of some embodiments ofthe invention. The designs, figures, and descriptions are non-limitingexamples of the embodiments they disclose. For example, otherembodiments of the disclosed device and/or method may or may not includethe features described herein. Moreover, disclosed advantages andbenefits may apply to only certain embodiments of the invention andshould not be used to limit the disclosed invention.

FIG. 1A shows a cable distribution plant 100A such as may be used fordistributing television and/or internet services. The cable plantincludes a head end 118 interconnected to a distribution node 112 viaoptical fiber 114. The optical fiber interconnects multiple distributionnodes 112 and each node supports multiple subscriber sites 102.

Subscriber sites 102, 106, 108 connect to a node via coaxial cable 110.Signals from the head end 118 provide subscriber sites with a televisionservice and/or an internet service via the nodes. For example, eachsubscriber site may include a cable modem 120 connected to a node via acoaxial cable. And, the cable modem may provide for interconnecting asubscriber site computer 130 with the head end.

It should be noted that, for clarity, downstream communications areshown taking place from the head end 118 and a fiber trunk 116 to thesubscriber 102. However, upstream communication from the subscriber 102to the head end 118 may also take place. For example, communicationsupstream may result from 1) computer 130 entries or 2) TV relatedcommands received from a TV 150 or from a set top box 140 (TV frontend).

FIG. 1B shows another view of the cable distribution plant 100B. Thecable plant includes an optical fiber 114 interconnecting a head end 118and a node. Multiple subscribers 102 are served from the node viacoaxial cable 110 which terminates at devices including subscribermodems 120.

In this cable distribution plant 100B noise 152-154 is shown movingupstream from the modems 120. This subscriber site noise may beaggregated 160 at the node. And, where there are multiple additionalnodes (see e.g., FIG. 1A), noise from these additional nodes 161 addswith the noise 160 and is aggregated 170 at the head end.

FIG. 2A shows another view of the cable distribution plant 200A. Here, amodem 120 is connected between a computer/digital appliance 131 and anode 112. Coaxial cable 110 interconnects the node and the modem and adata cable 212 such as Ethernet interconnects the modem and acomputer/digital appliance 131.

Within the modem 120 is a radio frequency noise source 204 and digitalelectronics 202. The digital electronics includes a modem transceiver203. As shown, noise 154 originates with subscriber modems 120. Invarious embodiments, a modem housing/enclosure 205 encloses the digitalelectronics and the radio frequency noise source. In various embodimentsa coaxial connector such as a coaxial port protrudes from the housing.And in various embodiments an AC mains power cord terminates at thehousing.

It is noted that a cable modem filter may be distributed. That is, themodem filter may include components/filters internal to the cable modemhousing/enclosure and components/filters external to the cable modemhousing/enclosure.

FIG. 2B shows a modem block diagram 200B. As seen, the modem includesdigital electronics 240 powered by a switching power supply 234. Inparticular, an AC power source 230 such as AC mains power sourceprovides power to the switching power supply via an EMI (ElectromagneticInterference) filter 232. An LC (inductor/capacitor) filter 236 followsthe switching power supply. Positive 238 and negative (common) 239 LCfilter outputs which may be referred to as rails or power rails provideDC power to the digital electronics 240.

FIG. 2C shows a power rail interconnection with the coaxial cable 200C.As mentioned, the digital electronics interconnects with the positiveand negative/common power rails of the LC filter. Embodiments mayinclude digital circuitry 249, 250. Digital electronics circuitry 249may provide a current path between power rail 239 and the coaxial cable110. And, digital electronics circuitry 250 may provide a current pathbetween power rail 238 and the coaxial cable 110.

In an embodiment, digital electronics circuitry 249 provides a currentpath between power rail 239 and a center conductor 260 of coaxial cable110. And, in an embodiment digital electronics circuitry 250 provides acurrent path between power rail 238 and the ground sheath 261 of coaxialcable 110. In some embodiments, both of these current paths exist.

FIG. 3 shows another view of the cable distribution plant 300. Thisplant is similar to the cable distribution plant of FIG. 2A. However,here an auxiliary filtering device 302 is located between the modem 120and the node 112.

In various embodiments the auxiliary filtering device 302 interconnectsthe shields of the coaxial cables 1100, 1101. In various embodiments,the auxiliary filtering device 302 interconnects the center conductorsof coaxial cables 1100, 1101. And in various embodiments, the auxiliaryfiltering device 302 interconnects both the shields and the centerconductors of coaxial cables 1100, 1101. Where the auxiliary filteringdevice 302 is connected directly to a modem port, for example using amale F type connector, annotated item 1100 is the modem port/coaxialconnector.

The auxiliary filtering device 302 may augment the filtering capacity ofthe modem's internal LC filter 236. In particular, the LC filter may bedesigned to provide filtering at or primarily at the frequency of theswitching power supply, for example at switching frequencies between 500KHz to 2 MHz. And, the auxiliary filter may be designed to providefiltering at or primarily at harmonics of the switching frequency, forexample in the 2 to 50 MHz range or in a range below 51 MHz.

In this manner, the LC filter 236 and auxiliary filtering device 302work together to filter the switching power supply noise. Here, themodem digital electronics are protected from switching power supplynoise by the LC filter and the head end 118 is protected from switchingpower supply noise by the auxiliary filtering device.

Notably, the LC filter 236 may be in a modem housing 205 while theauxiliary filtering device 302 may be located outside the modem housing.And notably, the LC filter is between the switching power supply 234 andthe modem digital electronics 240 while the auxiliary filtering deviceis between the modem and a node.

FIGS. 4A-C show a first auxiliary filtering device. As seen in 400A, thedevice includes a housing 402, an inductor such as a ferrite 404, and aninductor wire 406 coiled around the inductor 404. The inductor wire mayinterconnect the shields 410, 412 of coaxial devices, may interconnectthe center conductors 411, 413 of the coaxial devices, or mayinterconnect both the shields and the center conductors of coaxialdevices where coaxial devices include coaxial cables and coaxialconnectors.

In various embodiments, the auxiliary filtering device 400A includescoaxial cable connections 420, 422 such as male-male, female-female, andmale-female connections. The connections may be F-Type coaxialconnections such as a male connection with a central pin 499 forattachment to a modem and a female connection with a seizing pin 498 forattachment to a coaxial cable terminated with a male connector.

In an embodiment the inductor wire 406 is a coaxial cableinterconnecting both the shield conductor and center conductor of afirst coaxial devices with that of a second coaxial device. In anembodiment the inductor wire 406 is a micro-coaxial cable. Micro-coaxialcable outside diameters may vary from less than 1 mm to 2.5 mm. Microcoaxial cable outside diameter may be about 1.5 mm. In some embodimentsthe micro coaxial cable impedance is 75 ohms.

Tolerances here and elsewhere in this patent specification are plus orminus manufacturing tolerances, unit conversion tolerances, andmeasurement tolerances.

The inductor wire may pass through and/or be coiled around the inductorand the inductor may be an open or closed loop such as a closed loop inthe form of a toroid or shield bead.

For some embodiments of a ferrite bead or toroid, the impedance measuredin Ohms varies from 20 to 90 Ohms and in some embodiments may be 28 Ohmsat 10 MHz (+/−5 MHz), 45 Ohms at 25 MHz (+/−5 MHz), and 68 Ohms at 100MHz (+/−5 MHz). In an embodiment impedance varies from about 28 Ohms toabout 68 Ohms over a range of 10 MHz to 100 MHz.

For some embodiments where micro-coaxial cable is coiled on a ferritetoroid, at 5, 15, 25, and 50 MHZ for respective attenuations of 10, 14,16, 13 dB respective reactances are 167, 300, 308, 263 ohms, andrespective inductances are 5, 3.2, 1.9, 0.8 uh.

In an embodiment a micro-coaxial cable is coiled around a shield beadsuch that the inductor wire enters the bead passage 2 to 7 times.

FIG. 4B shows a cross-sectional drawing of a version of the firstauxiliary filtering device 400B. Within a housing 471 which may or maynot have a metal shroud 472 is a toroidal structure 467 about which amicro-coaxial cable 465 is coiled. One end of the filter 476 includes afemale F-Type connector 460 and another end of the filter 477 includes amale F-Type connector 462.

At the female connector end of the filter 476 the micro-coaxial cableend 464 is terminated 1) with the shield 468 in a first conductivesleeve including external port threads 474 and 2) with the centerconductor 480 in a coaxial sleeve insulator 472 located inside the firstconductive sleeve.

At the male connector end of the filter 477 the micro-coaxial cable end466 is terminated 1) with the shield 469 in a second conductive sleeveincluding internal connector threads 462 and 2) with the centerconductor 481 in a coaxial sleeve insulator 473 located inside thesecond conductive sleeve. The shroud 472 may be electricallyinterconnected with the male connector 462.

At the right of the figure is an end view of the filter 480. This viewis taken from the male connector end 477. Use of micro-coaxial cable 465permits the outside diameter of the filter 400B to be less than 20 mmand the length of the filter to be less than 58 mm.

Reduced shielding available for micro-coaxial cables may require a metalshroud 472 and the shroud may be electrically interconnected with acoaxial device shield such as that of a male coaxial connector. Further,use of micro-coaxial cable may influence the permeability and/or theimpedance specification of the inductor 467.

Micro-coaxial cable construction may include a center conductor, adielectric around the center conductor, an aluminum foil shield and/or ametallic wire braid with an outer polymer jacket such as a PVC jacket.The micro-coaxial cable may have an impedance of 75 Ohms. Use of foiland braid shields (dual shields) provides additional center conductorshielding.

FIG. 4C shows frequency response of an auxiliary filtering device. Thisparticular filter utilizes a single coil of dual shield 1.5 mm 75 Ohmmicro-coaxial cable about a shield bead having an impedance that variesfrom about 28 Ohms to about 68 Ohms over a range of 10 MHz to 100 MHz.In particular, it is seen that filter response is (0 dB) below 1 MHz and(−16 dB) at about 25 MHz afterwhich filter response changes to about −13dB at about 50 MHz. As discussed earlier, this range of frequencyresponse from about 6 MHz to about 30 MHz protects the head end 118 fromnoise in the form of harmonics emanating from the switching power supply234.

In some embodiments capacitive effects owing to use of micro-coaxialcable and or micro-coaxial cable coiled around a ferrite such as theindicated micro-coaxial cable 406 and/or ferrite 404 result in filterresponse that is about flat between 15 and 35 MHz.

FIGS. 5A-B show auxiliary filtering device 500A-B. Like the device ofFIG. 4A, these devices condition the signal on a coaxial cable shield orground conductor.

The filter of FIG. 5A is similar to the filter of FIG. 4A. Inparticular, the FIG. 5A filter includes a metallic filter enclosure 402and within the enclosure an inductor wire 406 coiled around an inductorsuch as a ferrite or ferrite toroid 404. Coaxial devices at opposed endsof the filter 420, 422 include respective shields 410, 412 and centerconductors 411, 413 with the center conductors interconnected by a wire405 and the shield conductors interconnected by the inductor wire. Invarious embodiments, the coaxial devices 420, 422 may be coaxial cableconnections such as F-Type coaxial connections and may be as male-male,female-female, and male-female connections.

The filter of FIG. 5A includes features that may not be found in FIG.4A. In particular, the FIG. 5A filter may, as shown, include anelectrical connection/wire 502 between the enclosure 507 and the shieldof a connector 503 such as connector 420. In some embodiments connector420 is attached/connected to the modem 120. Further, this filter mayinclude a capacitor 504 connected at one end to the inductor wire 505and connected at the other end to the connector shield 503. Thisembodiment obviously provides an LC (inductor-capacitor) filter.Capacitor values may vary between 10 and 5000 pf. Capacitor values mayvary between 100 and 1000 pf. Capacitor values may vary from 200 to 500pf. A capacitor value of about 330 pf may provide a notch around 20 MHzwhen attached on a third winding of an inductor wire in a filter withfour windings on a toroid.

The filter of FIG. 5B is similar to the filter of FIG. 5A. Inparticular, the FIG. 5B filter includes a metallic filter enclosure 402and within the enclosure an inductor wire 406 coiled around an inductorsuch as a ferrite or ferrite toroid 404. Coaxial devices at opposed endsof the filter 420, 422 include respective shields 410, 412 and centerconductors 411, 413 with the center conductors interconnected by a wire405 and the shield conductors interconnected by the inductor wire.

While the capacitor of FIG. 5A was located between the inductor wire 505and the shield 503, the capacitor of FIG. 5B is located between theinductor wire 505 and the enclosure 520. This arrangement removes theconnection between the shield 503 and the capacitor 504 and replaces itwith a connection between the enclosure 402 and the capacitor 520.Again, this arrangement provides yet another LC (inductor-capacitor)filter.

FIG. 6A-B show auxiliary filtering devices 600A-B. Unlike the filters ofFIGS. 4A,B and FIGS. 5A,B, the filters of FIG. 6A-B condition signals onboth a coaxial shield and a coaxial cable center conductor.

The filter of FIG. 6A is somewhat similar to the filters of FIG. 5A-B.In the filter of FIG. 6A, a filter enclosure 402 covers a first inductorwire 602 coiled around an inductor such as a ferrite or ferrite toroid404. Coaxial devices at opposed ends of the filter 420, 422 includerespective shields 410, 412 and the inductor wire 602 completes thecircuit between the shields. A second inductor wire 603 is also coiledaround the inductor and in some embodiments the inductor is coiled in adirection opposite that of the first inductor. The second inductorcompletes the circuit between the center conductors 411, 413 of thecoaxial devices 420, 422. In various embodiments, the coaxial devices420, 422 may be coaxial cable connections such as F-Type coaxialconnections and may be as male-male, female-female, and male-femaleconnections.

In addition to the first and second inductor wires 602, 604, the filterof FIG. 6A includes a capacitor 504, One end of this capacitor isconnected 614 to the shield of connector device 422 and the other end ofthe capacitor is connected 615 to the center conductor of conductordevice 422.

This arrangement provides an LC (inductor-capacitor) filter thatconditions the signal on each of the shield and the center conductor. Invarious embodiments using oppositely wound inductor wires 602, 603 thisfilter cancels out or attenuates shield signals that are simultaneouslyrepeated on the center conductor.

FIG. 6B shows a filter similar to that of FIG. 6A. In the figure atoroidal ferrite 650 having two windings is shown in a filter enclosure402. A first winding 651 wound in a first direction interconnects theshields 410, 412 of coaxial devices 420, 422. A second winding 652interconnects the center conductors 411, 413 of coaxial devices 420,422.

In FIGS. 4A, 4B, 5A, 5B, 6A, 6B various embodiments provide for theshield 410 of connector 420 to be connected to a metallic enclosure 402.The metallic enclosure may be wrapped around one end or wrapped aroundboth ends of the connector. The shield may be connected to the metallicenclosure at one end of the metallic enclosure or at both ends of themetallic enclosure. And, in these same figures, various embodimentsprovide for the shield of connectors 420, 421 to be disconnected fromthe metallic enclosure 402.

FIG. 7 shows a two cable filtering solution 700. Here, a modem mainspower cable (120 VAC) 710 and a modem coaxial cable 110 are passedthrough a ferrite loop such as a split 704, 705 toroid 702. When closedthe split torroid provides a continuous magnetic path around the coaxialand power conductors. In this filter, noise on the coaxial shield and toa lesser extent noise on the coaxial center conductor is injected intothe power cord.

FIGS. 8A-C show an isolating filter and its printed circuit boards800A-C. In various embodiments the filter may be made with a maximumouter diameter of less than 16 mm and a maximum length of less than 43mm.

FIG. 8A shows the isolating filter 800A. A male F-Type connector 872 isat one end and a female F-Type connector 871 is at an opposite end. Inthe figure, 802-806 are insulators and 811-812 are ferrites. In thefigure 820 is a coaxial cable such as an RG-179 coaxial cable and 861 isa shield of the coaxial cable 820. In the figure 821-824 are centerconductors where 821 is an F-Type female connector seizing pin and822-823 are coaxial cable center conductors and 824 is a male F-Typeconnector center pin. In the figure 831 is an inner metal shell and 832is an outer metal shell. In the figure 841 and 842 are printed circuitboards. In the figure 851 is a metallic and/or plated metal (e.g., zinc,nickel or similar) bridge interconnecting the outer traces of theprinted circuit boards. In various embodiments, the coaxial connectors871, 872 may be coaxial cable connections such as F-Type coaxialconnections and may be as male-male, female-female, and male-femaleconnections.

The center conductors of this isolating filter 821-824 pass a centerconductor signal through the filter without attenuating or otherwiseaffecting the signal. However, the signal on the shield of the coaxialcable 861 is processed through devices including a high pass filter.

The signal reaches the coaxial cable braid/shield 861 when it isconducted by the female end 871 inner shell 831 to the coaxial cablebraid by a conductor or clip 881 extending therebetween the braid andthe inner shell. The coaxial cable then passes through a first ferrite811. And, beyond this ferrite the signal is passed to a first printedcircuit board 841 via the coaxial cable braid 861.

FIG. 8B shows the first printed circuit board (“PCB”) 800B. The PCB hasnested cylindrical or looped traces, one 804 inside the other 802. Thecoaxial cable braid 861 is soldered to the inner trace of this PCB.Capacitors 811, 813 and resistors 812, 814 interconnect the two traces.Notably, the capacitors and resistors may be more or less numerous andthey may be arranged in any order.

FIG. 8C shows a second PCB 800C. The PCB has nested cylindrical orlooped traces, one 834 inside the other 832. The coaxial cable braid 861is again soldered to the inner trace 834 of the second PCB. Capacitors841, 843 and resistors 842, 844 interconnect the two traces. Notably,the capacitors and resistors may be more or less numerous and they maybe arranged in any order.

Total resistance across the traces of the first and second PCB's 850,851 may vary from about 10 to 1000 Ohms or may be less that about 100Ohms. Total capacitance across the traces of the first and second PCB'smay vary from about 10 to 1000 pf or may be less than about 100 pf.Between the two PCB's is a second ferrite 812 through which the coaxialcable 861 passes.

The signal leaves the first PCB inner trace 804 and moves via theresistor(s) and capacitor(s) to the outer trace 802 where the zincbridge 851 interconnects the outer trace of the first PCB 802 with theouter trace of the second PCB 832. The second PCB outer trace isconnected to the male end 872 outer shell 832.

In parallel with this signal path via the coaxial cable braid 861 is asecond signal path interconnecting the inner shell 831 and outer shell832. This second signal path comprises a capacitor created by an overlap“d” created where the inner shell 831 is inserted in the outer shell832. In various embodiments the resulting capacitance is about 100 to3000 pf and in some embodiments the capacitance is about 1500 to 1900pf.

With the auxiliary filtering devices of FIGS. 4A-B, 5A-B, and 6A-B, useof micro coaxial cable may enable construction of a relatively smallfilter with a maximum diameter of less than 19.3 mm and a maximum lengthof less than 57.5 mm. Where a male end of the filtering device will bescrewed onto a female modem port at the rear of the modem, small filtersize is desirable to hide the filter from view and to reduce modemstand-off distance required by filter length. In addition, modem labelsnear the modem port can be hidden by filters having diameters largerthan 19.3 mm.

With the auxiliary filtering device of FIG. 7, the toroidal clam shell700 is closed around the AC power cable and the modem coaxial cablewhich enables the filter to be placed conveniently out of sight and awayfrom the modem port at the rear of the modem.

And, with the isolating filter of FIG. 8A, use of small PCB's enablesconstruction of a relatively small filter with a maximum diameter ofless than 16 mm and in some embodiments less than 19.3 mm. The maximumlength of this filter is less than 43 mm.

We turn now to alternative packaging or cases for the auxiliaryfiltering devices mentioned above. Alternative packaging may includepackaging with other than that having a circular cross-section,packaging including coaxial connectors that are not aligned, and/orpackaging having an interface other than a coaxial cable connectorinterface with adjacent equipment such as with a modem.

FIG. 9A shows an auxiliary filtering device mounted to a modem 900A.FIG. 9B shows details of the mounting of the filtering device 900B.

In various embodiments the auxiliary filtering device 901 is packaged ina case or housing 904 near the case right side 916. When viewed from thefront the case has a somewhat “L” shape. As seen, the device is mountedto a modem 902 with modem case or housing 987, back-face 905 andback-face vertical rims 906, 908.

The device 901 and the modem 902 connect at a coaxial cable connection903 that includes a modem F-Type connector 926 extending from the backface of the modem 905 and a device mating male connector 922 extendingfrom a back face of a leg of the device “L” 907. The device connectorthat attaches to the modem may be referred to as the device modemconnector 922 and the device connector that attaches to the cabledistribution system may be referred to as the device signal connector.Notably, the connectors may be coaxial connectors other than F-Typeconnectors and the connectors may be screw-on or push-on.

A female F-Type connector 924 protrudes from the front face where thelegs of the device “L” meet 909, 915. Connected between the device maleand female connectors 922, 924 circuit elements within the case 904, forexample those mentioned above, provide a filter. And as mentioned above,the device female connector 924 is for connection with a cabledistribution system.

A second connection between the modem 902 and the device 901 may bemade. This second connection may support of the device and/or to preventrotation of the device relative to the modem. In an embodiment, thesecond connection utilizes a groove 920 in the back face of the oppositeleg of the device “L” 921. When the device is properly mounted on themodem, the groove straddles a vertical rim 908 of the modem. In variousembodiments contact between the groove and the rim resists motion of thedevice and rotation of the device relative to the modem.

In some embodiments: the groove in the device may be wide enough to fitover the modem back-face rim for different width modems; the inner mostside wall of the groove may prevent the device from rotating by buttingup against the inside wall of the modem rim for the thinnest modem; theouter most side wall of the groove may prevent the device from rotatingby butting against the outside wall of the modem rim for wide modems.

FIGS. 9C-E show front, bottom, and side views of the auxiliary filterdevice.

In the front view of FIG. 9C the “L” shape of the device is seen. Withinthe case 901 is a circuit element such as a toroidal transformer 913 andprotruding from the case are coaxial cable connectors 922, 924 mentionedearlier. A coaxial or micro-coaxial cable 923 is wrapped around thetoroid 913 and is coupled (not shown) directly or indirectly to each oftwo coaxial connectors 922, 924.

Notably, in this device 901 the connectors point in opposite directionssuch that the device modem connector 922 projects from a back-face 907of the device and the device cable distribution system connectorprojects from a front of the device.

In the bottom view of FIG. 9D, the micro-coaxial cable 923 is wrappedaround the toroid 913 and has ends coupled to the connectors 922, 924.Micro-coaxial cable 917 connects directly or indirectly the device maleconnector 922 with the device female connector 924. As seen, the toroid913 is located above the device female connection 924. Also shown inthis view is the modem 902 and a modem ridge or projection 908 that fitswithin the groove 920 of the device.

In the side view of FIG. 9E, the device female connector 924 is shownprojecting from the case 901. Micro-coaxial cable 919 connects directlyor indirectly the device female connector 924 and the device maleconnector 922. In addition, the coaxial or micro-coaxial cable 923wrapped around toroid 913 connects the device female connector 924 tothe device male connector 922 (not shown in this view).

FIG. 10A shows an auxiliary filtering device mounted to a modem 1000A.FIG. 10B shows details of the mounting of the filtering device 1000B.

The auxiliary filtering device 1001 is packaged in case 1004. Whenviewed from the front the case has a somewhat “i” shape. The device ismounted to a modem 902. Notably, the case “i” includes both a dot 1025and a stem 1027. The device and the modem connect at a coaxial cableconnection 903 that includes a modem F-Type connector 926 extending fromthe back face of the modem 905 and a device mating male connector 922extending from a back face of the stem of the “i” 1021. A toroidalinductor may be located in the “dot” of the “i” shaped case.

A female F-Type connector 924 protrudes from a front face of the stem ofthe “i.” Between the device male and female connectors 922, 924, circuitelements within the case 1004, for example those mentioned above,provide a filter. And as mentioned above, the device female connector924 is for connecting with a cable distribution system.

A second connection between the modem 902 and the device 1001 may bemade. This second connection may support the device and/or to preventrotation of the device relative to the modem. In an embodiment, thesecond connection utilizes a groove 920 near the back face of the stemof the “i” 1012. Sliding in the groove are rails 1014 of a right-angleclip 1013. The clip is movable in the groove such that a clip hasp 1016moves with respect to the modem to accommodates varying modem geometriessuch as a thicker modem. The clip hasp laps over the modem side 1018 andmay be fixed to the modem side by a suitable fixture such as a pin,plug, screw or the like 1010.

When the device is properly mounted on the modem, the clip hasp 1016 isfixed to the modem 902 which, together with the coaxial cable connection903 using coaxial connectors 922, 926, supports and prevents rotation ofthe device 1001 relative to the modem.

FIGS. 10C-D show front, bottom, and side views of the auxiliary filterdevice 1000C-D. FIG. 10E shows a clip and a fastener 1000E.

In the front view of FIG. 10C the “i” shape of the device is seen withthe bulbous end being the dot 1025 and the shank being the stem 1027.Within the case 1001 is a circuit element such as a toroidal inductor1030 and protruding from the case are coaxial cable connectors forconnecting with the modem 922 and for connecting with a cabledistribution cable 924. A coaxial or micro-coaxial cable 1032 wrappedaround a toroid 1030 is coupled directly or indirectly to the devicecoaxial connector 922 that mates with the modem coaxial connector 926.

In the bottom view 1000D shown in FIG. 10D, the connection of the devicemale connector 922 to the modem female connector 926 is visible. Acoaxial or micro-coaxial cable 1032 wrapped around a toroid 1030 iscoupled at one end directly or indirectly to the coaxial connector 922that mates with the modem coaxial connector 926. Another end of thecoaxial cable 1034 is coupled directly or indirectly to the coaxialconnector 924 that attaches to the cable distribution system. In thisview the toroid 1030 is at the device left end and the device femaleconnector is at the right end. Also shown in this view is the modem 902and a modem back-face ridge or projection 908 that fits within aback-face groove 920 of the stem of the “i.”

In the side view 1000DD of the device 1001 shown in FIG. 10D, theconnector 924 that attaches to the cable distribution system is seen.Also shown is a portion of the bulbous end of the device (dot of the“i”) 1025, the shank (stem of the “i”) 1027, and the groove 920 in whichthe clip 1016 rides with rails 1014 inserted in the groove.

FIG. 10E shows the clip 1012 and fastener 1010. The clip has aright-angle shape with the shorter leg including a “U” shaped notch 1049that forms opposed rails 1014 that ride within the grooves 920 of thedevice. The longer leg of the “U” is like a hasp 1016 that laps or laysover the edge of the modem 902. The hasp may be fixed to the modem sidevia the fastener 1010.

FIG. 11A shows an auxiliary filtering device mounted to a modem 1100A.FIG. 11B shows details of the mounting of the filtering device 1100B.

The auxiliary filtering device 1101 is packaged in case 1104. Whenviewed from the front the case has a left 1137 to right 1139 linearshape. The device is mounted to a modem 902. The device and the modemconnect at a coaxial cable connection 903 that includes a modem F-Typeconnector 926 extending from the back face of the modem 905 and a devicemating male connector 922 extending from a back face 1121 of the linearshape. A toroidal inductor may be located in right side 1139 of thelinear case.

A female F-Type connector 924 protrudes downward from the left side ofthe device case 1137. Circuit elements within the case 1104 may includethose mentioned above and may provide a filter. As mentioned above, thedevice female connector 924 is for mating with a cable distributionsystem cable.

A second connection between the modem 902 and the device 1101 may bemade. This second connection may support the device and/or to preventrotation of the device relative to the modem. In an embodiment, thesecond connection utilizes a channel 1110 at the back face 1135 of theright side 1139 of the linear case 1104. The channel engages a ridgeback-face ridge 908 of the modem case. The ridge and channel engagementsupport the device and prevent the device from rotating relative to themodem 902.

FIGS. 11C-D show front, bottom, and side views of the auxiliary filterdevice 1100C-D.

In the front view of FIG. 11C the linear shape of the device is evidentwhen viewed from the front. Within the case 1104 is a circuit elementsuch as a toroidal inductor 1130 and protruding from the case arecoaxial cable connectors for connecting with the modem 922 and forconnecting with a cable distribution cable 924. A coaxial ormicro-coaxial cable wrapped 1133 around a toroid 1130 is coupled 1132directly or indirectly to the coaxial connector 922. The other end ofthe coaxial cable is coupled 1134 directly or indirectly to the coaxialconnector 924. Also, the device channel 1110 at the back-face of thedevice 1135 engages the rail 908 (not shown) of the modem.

Notably, in this device 1101 the device connectors point at 90 degreesto each other such that the device modem connector 922 projects from aback-face 1145 of the device and the device cable distribution connectorprojects from a bottom 1147 of the device.

In the bottom view 1100D shown in FIG. 11D, the connection of the devicemale connector 922 to the modem female connector 926 is visible. Here,the coaxial or micro-coaxial cable connects at one end to the devicemodem connector 922 and at the other end to the device cabledistribution system connector 924. In this view the toroid is at theright end of the device and the device female connector is at the leftend of the device. Also shown in this view is the modem 902 and a modemback-face ridge or projection 908 that fits within a device groovedchannel 1110.

In the side view 1100DD shown in FIG. 11D, the connector 924 thatattaches to the cable distribution system is seen. Also shown is thebulbous end of the device (dot of the “i”) 1025, the shank (stem of the“i”) 1027, and the groove 920 in which the clip 1016 rides with rails1014 inserted in the groove. In various embodiments the groove makes aninterference fit with the rim. In various embodiments the groovedimension is larger than the rail dimension such that there is limitedmotion of the device with respect to the modem.

Notably, FIGS. 9A, 10A, and 11A describe auxiliary filtering devices901, 1001, 1101 with two points of attachment to a modem. These pointsof attachment are a coaxial connector attachment 903 and a claw likeengagement 920, 1012, 1110. Because the device incorporates both themodem coaxial connection and the modem claw connection, and becausethese connections are spaced apart, they provide structural support tothe device and prevent the device from rotating relative to the modem902. Embodiments of the claw like engagement may engage a modemback-face rim, or a modem side panel 1018. These features may also bereferred to as a modem back-face rim and device groove engagement or asa device hasp and modem side panel engagement.

Notably, the above mentions of a toroid or toroidal inductor utilize butone of the configurations of the filters described herein. This is notlimiting as any of the filtering components and filtering circuitsdescribe herein may be used in lieu of the toroid.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be apparent to those skilledin the art that various changes in the form and details can be madewithout departing from the spirit and scope of the invention. As such,the breadth and scope of the present invention should not be limited bythe above-described exemplary embodiments, but should be defined only inaccordance with the following claims and equivalents thereof.

What is claimed is:
 1. A distributed filter system communicates with acable distribution system that includes a head end and distributionnodes, the distributed filter system comprising: a discrete componentfilter connected to a male coaxial connector and a female coaxialconnector; the discrete component filter for fitment to a modem viafirst and second connections; the first connection utilizes the malecoaxial connector and a mating modem connector and the second connectionutilizes a filter claw that engages a modem housing; the modem housingincluding a switching power supply and digital electronics; theswitching power supply for receiving alternating current (AC) mainspower from an AC supply via an electromagnetic interference (EMI) filterand the digital electronics for receiving a switching power supplyoutput from the switching power supply via an inductive and capacitive(LC) filter for filtering noise at a switching power supply frequency;and, the discrete component filter for filtering noise at harmonics ofthe modem switching power supply frequency; wherein multiple discretecomponent filters communicate with respective modems at subscriber sitesto protect the head end from switching power supply harmonic noiseotherwise aggregated by the distribution nodes and passed to the headend.
 2. The system of claim 1 wherein the discrete component filtercomprises: a modem back-face vertical rim that engages a groove in thediscrete component filter.
 3. The system of claim 1 wherein the discretecomponent filter comprises: a right-angle clip that engages a groove inthe discrete component filter and adjusts to accommodate varying modemthicknesses in the modem.
 4. The system of claim 1 wherein the harmonicnoise is carried by a coaxial shield of a coaxial cable coupled with themodem.
 5. The system of claim 1 wherein the harmonic noise is carried bya coaxial center conductor of a coaxial cable coupled with the modem. 6.The system of claim 1 wherein the discrete component filter includes amicro-coaxial cable wrapped around a toroid, a first end of themicro-coaxial cable connected to the male coaxial connector and a secondend of the micro-coaxial cable connected to the female coaxialconnector.
 7. A method of providing a device for reducing head end noiseresulting from the aggregation of modem switching power supply harmonicnoise at distribution nodes, the method comprising the steps of:providing modem electronics including a switching power supply and atleast one of an EMI filter and a LC filter included in a case; providinga modem F-type connector extending from the case; providing an in-lineexternal filter outside the case and having first and second F-typeconnections; fixing the external filter when the extending F-typeconnector is mated with the first F-type connection and when theexternal filter is coupled to the case; connecting the second F-typeconnection to a subscriber device; and filtering, by the externalfilter, noise at harmonics of a switching power supply frequency,wherein multiple external filters communicate with respective modems atsubscriber sites to protect the head end from switching power supplyharmonic noise otherwise aggregated by the distribution nodes and passedto the head end.